Patients with type A, B, or AB blood are at significantly greater risk for coronary heart disease than those with type O blood, researchers found.

Action Points

Patients with type A, B, or AB blood are at significantly greater risk for coronary heart disease (CHD) than those with type O blood, a study has found.

Note that the associations between blood type and CHD risk were not modified by age, physical activity, alcohol consumption, smoking status, or diabetes history in men or women.

Patients with type A, B, or AB blood are at significantly greater risk for coronary heart disease (CHD) than those with type O blood, researchers found.

Two large, prospective cohort studies showed those with a non-O blood type had an age-adjusted hazard ratio of 1.09 (95% CI 1.03 to 1.17, P=0.005) for risk of developing CHD, according to Lu Qi, PhD, of the Harvard School of Public Health, and colleagues.

A meta analysis of an additional six past cohorts also showed a significant pooled relative risk for CHD in patients with non-O blood type of 1.11 (95% CI 1.05 to 1.18, P=0.001), Qi and co-authors wrote in the August 14 issue of Arteriosclerosis, Thrombosis, and Vascular Biology.

"It has long been acknowledged that human ABO blood type might affect the risk factors of cardiovascular disease," the authors noted in their introduction. To further explore the issue, they gathered data through the Nurses Health Study -- a cohort initiated in 1976 that included 62,073 women ages 30 to 55 at baseline -- and the Health Professionals Follow-up Study -- a second cohort initiated in 1986 that included 27,428 men ages 40 to 75 at baseline. Those in each study were followed up to 2006.

Participants answered questionnaires on health data and lifestyle, as well as periodic food frequency data. They also were asked to report their blood type and Rh Factor (negative or positive), if known.

Measures were adjusted for age, smoking status, body mass index, alcohol intake, parental history of CHD before age 60, aspirin use, menopausal status and hormone use in women, history of hypertension, history of high blood cholesterol, and history of diabetes.

The researchers also conducted a meta-analysis of seven studies consisting of a combined 114,648 mostly white men and women.

A combined 2,055 cases of CHD occurred in the two cohorts, while there were 5,741 cases of CHD in the meta-analysis.

Among participants in the cohort, those with type O blood were significantly less likely to develop CHD when compared against types B (adjusted HR [aHR] 1.11, 95% CI 1.01 to 1.23) and AB (aHR 1.23, 95% CI 1.10 to 1.37), with a trend toward a higher risk for patients with type A blood (1.05, 95% CI 0.98 to 1.13).

Associations between blood type and CHD risk were not modified by age, physical activity, alcohol consumption, smoking status, or diabetes history in men or women, the authors wrote. However, BMI and blood type had a positive interaction with CHD risk in women at P=0.026.

Differences in Rh type were not significantly associated with CHD risk.

The results of the meta-analysis showed a trend for the association between non-O blood type and CHD risk at a pooled relative risk of 1.06 (95% CI 0.96 to 1.17).

The authors noted one of the included studies indicated a significant inverse association with non-O blood type and CHD risk. After excluding the outlier study, the remaining six studies showed a significant association between non-O blood type and CHD risk with a pooled relative risk of 1.11 (95% CI 1.05 to 1.18, P=0.001).

"The highest risk was observed for blood group AB, followed by blood groups B and A," Qi and colleagues wrote, adding that a possible mechanism of action has been seen in studies that "reported that plasma levels of factor VIII-VWF complex in non-O individuals were approximately 25% higher than in group O individuals."

They explained that the von Willebrand factor (VWF) mediates platelet adhesion to the vascular wall and also participates in platelet aggregation and in development of atherosclerosis.

The study has important implications for healthcare professionals and patients, said Jeffrey Berger, MD, of the NYU Langone Medical Center in New York City.

â€œI would tell a patient that, based on some nicely done, elegant studies, we know they are at increased or lower risk based on their blood type,â€ he said in an email to MedPage Today and ABC News.

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